1. Field of the Invention
The present invention relates to a mobile communication system and a communication method, and more particularly, to a reservation based mobile communication system, mobile terminal equipment, and communication method to which code division multiple access (CDMA) is applied.
2. Description of the Related Art
Conventionally, a mobile communication system which employs a reservation based access control in a frequency division multiple access (FDMA) scheme is known, for example, as described in IEEE Transactions on Communications, Packet Switching in Radio Channels: “Part3-Polling and (Dynamic) Split-Channel Reservation Multiple Access”, COM-24, 8, (1976), pp. 832-845 (hereinafter called “prior art publication 1”).
In the reservation based access control, each of mobile terminals having a request for data transmission reserves a traffic channel to a base station through a reservation packet. The base station, after scheduling traffic channels and transmission timing (time slots) to be assigned to these mobile terminals, notifies each of the mobile terminals of transmission timing to be used on an assigned traffic channel through a reply packet. According to this reservation based access control, collision of packets on the traffic channel can be basically avoided.
As another example of reservation based control type communication system, for example, JP-A-6-311160, corresponding to U.S. patent application Ser. No. 08/230,773 (hereinafter called “prior art publication 2”) has proposed such a communication system based on a time division multiple access scheme.
However, in the mobile communication systems in which the reservation based access control is applied to FDMA and TDMA schemes, as proposed by prior art publications 1 and 2, since respective mobile terminals send reservation packets through a reservation channel asynchronously with each other, a plurality of reservation packets can collide with a high possibility. Thus, repetitive retransmission of reservation packets obliged by the collision of packets constitutes a main cause of degrading the throughput of the entire communication system.
Meanwhile, as a standard for FPLMTS (Future Public Land Mobile Telecommunication Systems), the adoption of the code division multiple access scheme is regarded as promising. A CDMA mobile communication system has been proposed, for example, in JP-A-7-38496 corresponding to U.S. patent application Ser. No. 08/375,679 (hereinafter called “prior art publication 3”). However, prior art publication 3 does not provide any useful information for solving the problem of a degraded throughput in the reservation based access control.